Influence of physical and chemical properties on the low‐frequency complex conductivity of peat

Abstract

Organic layers are heterogeneous in space and their composition changes over time. This poses challenges to ecohydrologists, subsurface hydrologists and ground engineers in characterizing subsurface peat structures and predicting their behaviour over time. Peat deposits can be characterized by performing electrical surveys, provided that the complex conductivity of peat is understood and connected to its physical and chemical properties. Low-frequency (0.1-1000 Hz) induced polarization measurements were carried out to investigate the correlation between the chemical and physical properties of several peat samples and their electrical properties. A Cole-Cole model was fit to the peat spectra to obtain the model parameters and study their relationship with the sample properties. All the samples were characterized by analysing their degree of humification, water content, organic content, cation exchange capacity, pH and conductivity of the pore-fluid. Two significant correlations between physical, chemical and electrical properties are found. The peat bulk conductivity is directly correlated with the pore fluid conductivity, whereas the degree of humification of peat shows an inverse correlation with the phase angle. This study presents results that have implications for peatland characterization with frequency dependent or single frequency analysis of induced polarization measurements.is an increase of charged organic acid functional groups. Reported values for moss peats show that CEC increases from 100-124 cmol/kg when the humification increases from not decomposed (H1) to moderate decomposed (H5) peat (Puustjarvi and Robertson 1975). During the decomposition of the organic matter, peat also undergoes a structural change, going from a fibrous structure to a granular isotropic state. This loss of structure reduces the amount of water that can be retained by the peat (Landva and Pheeney 1980). Moreover, changes in porosity have an influence on the conductivity of peat, as pore-throat diameters and pore geometry of water-saturated geo-materials contribute significantly to both in-phase and out-of-phase conduction at low-frequencies (Scott and Barker 2003). Cosenza et al. (2007) showed that changes in both water content and texture affect the spectral induced polarization response during the shrinkage of clay; textural changes are determined by loss of water in the micropores and thus the low-frequency polarization is not controlled by macropores (Ghorbani et al.

Multi‐scale analysis of electrical conductivity of peatlands for the assessment of peat properties

“…However, Ponziani et al . () did not find correlations between CEC and σ′ or σ″ (non‐significant coefficients of determination of −0.1 and −0.14, respectively). They measured σ′ and σ″ of water‐saturated samples, whereas our samples included unsaturated conditions as well.…”

“…The dominant effect of σ w on σ′ was described by Ponziani et al . () as well, who also used a multisite dataset. Thus, a multisite analysis of σ′ is not suitable for determining the properties of peat that are used to describe its condition.…”

“…Ponziani et al . () found a negative correlation between the DD and the phase angle (phase shift between real and imaginary voltage), but did not observe a correlation of DD with σ″ or σ′. Therefore, the question remains as to whether σ′ and σ″ are correlated with DD and whether the correlations are positive or negative.…”

Induced polarization applied to biogeophysics: recent advances and future prospects

“…() reported a strong correlation between peat CEC and quadrature conductivity (IP parameter), while Ponziani et al . () could not find any correlation between the IP response and various sample characteristics such as decomposition state, water content, organic content and CEC.…”

Estimation of sediment texture from spectral induced polarisation data using cluster and principal component analysis

“…a,b; Grunat, Slater and Wehrer ); organic fraction properties (Ponziani et al . ), including also the presence of bacteria (Abdel Aal et al . ) or contaminants (Vanhala ; Martinho, Almeida, and Senos Matias ; Saltas et al .…”